This invention relates to a sensor device for detecting the degree of wetting and/or soiling of a light-transmissive pane, such as a window pane, in a motor vehicle having a housing including radiation guide, or conductor, elements that can be coupled to an inner surface of the pane, a radiation emitter and radiation receiver, each of which is provided with a collecting/directional element coupled to in the respective radiation guide element, with the optical axes of the collecting/directional elements being arranged at acute angles to the pane, and with the radiation guide elements being arranged flush to a wall of the housing facing the pane on a side facing away from the radiation emitter and/or radiation receiver.
Furthermore, this invention relates to a method of producing a sensor device for motor vehicles which is attached by a transparent coupling medium to an inside surface of the pane in the motor vehicle.
German Patent. 40 27 367 C1 describes a sensor device for detecting the degree of wetting of a window pane in a motor vehicle, including a plurality of optical components. In addition to a reflector that reflects radiation of a radiation emitter, there is a radiation guide element on whose edge face a mirrorized coating is provided, so that the radiation strikes the window pane at a predetermined angle of incidence. A radiation receiver is positioned so that radiation that is totally reflected on the window pane strikes the radiation receiver after being guided through the same radiation guide element. In an area between the radiation receiver and the window pane there is a layer of a non-transparent material with which it is possible to reduce the ambient light radiation, which would falsify the result of the measurement. It is disadvantageous of this known sensor device that the radiation emitted by the radiation emitter undergoes repeated necessary reflections before striking the window pane. This leads to a reduced radiation yield and negatively affects a tolerance sensitivity of the radiation receiver and the radiation emitter. Furthermore, this known sensor device requires a relatively complex design.
German Patent 197 13 910 C1 describes a sensor device for detecting the degree of wetting of a pane on a motor vehicle, providing a one-piece radiation guide element with recesses arranged on a side facing away from the window pane, and a radiation emitter and a radiation receiver mounted in each recess. One disadvantage of this known sensor device is that multiple reflections are provided in the radiation guide element, leading to a reduction in radiation yield. Furthermore, no shielding or covering measures are provided to prevent detection of unwanted ambient radiation.
German Patent 40 06 174 C1 describes a sensor device for detecting the degree of wetting of a pane in a motor vehicle, where a one-piece radiation guide element is provided, having respective collecting lenses for a radiation emitter and a radiation receiver. A layer of a reflective material is applied to a top or bottom side of the radiation guide element in an area between the projecting collecting lenses, so that beams emitted by the radiation emitter can be directed toward the radiation receiver by multiple reflections. However, this yields a relatively long beam path, with necessary multiple reflections resulting in a reduction in radiation yield.
An object of the present invention is to provide an improvement to a sensor device for detecting the degree of wetting of a pane of a motor vehicle such that a compact and simple structure of the sensor device is achieved in an uncomplicated manner while an improvement in optical properties is achieved.
Furthermore, it is an object of the present invention to provide a method of producing a sensor device that can be carried out inexpensively and by simple manufacturing technology.
According to principles of this invention, a sensor device of the general type set forth in the opening paragraphs above includes a separate radiation guide element for each of the radiation emitter and the radiation receiver, with the radiation guide elements being connected as one piece with a wall.
A particular advantage of the sensor device of this invention is that a path of radiation between the radiation emitter and the radiation receiver is relatively short, and, with the exception of a reflection at an outside surface of the pane, there is no unwanted reflections required. Thus light efficiency can be greatly improved. Because the radiation guide elements are formed as one piece with the wall of a housing, the wall has the function of supporting the radiation guide elements while providing a radiation shield, since it is not transparent, so as to prevent unwanted penetration of ambient light into the housing.
According to a particular embodiment of this invention, a blocking element arranged between the radiation guide elements reduces the amount of ambient radiation entering from the environment. The radiation guide elements need not be directly connected to one another, so they can be structured in a manner that saves on material and space.
According to a particular embodiment of this invention, the non-transparent blocking element is part of the wall of the housing which faces the pane and has openings in which the individual radiation guide elements are mounted, each to have a surface flush with a surface of the wall. The wall and the radiation guide elements together advantageously form a carrier module which is placed like a cover on a pot-shaped part of the housing and can be connected to it in a form-fitting manner and/or by gravity. This makes it possible to greatly reduce the number of required components.
According to one embodiment of the sensor device of this inventions, the radiation emitter and the radiation receiver are arranged on a common circuit board, with optical axes thereof being oriented perpendicular to a pane with which the sensor device is to be used. The radiation guide elements of the sensor device are preferably arranged in a V-shape to the pane and are structured so that they are inclined at an acute angle to the pane for creating total reflection of the beams emitted by the radiation emitter at the outside surface of the pane. The resulting non-optimal alignment of the radiation receiver or radiation emitter with regard to radiation inlet or outlet faces of the radiation guide elements is thus compensated at least in part by the fact that the radiation path is relatively short and is free of necessary reflections. Because the radiation emitter and the radiation receiver are arranged flat on the circuit board, assembly of the circuit board is simplified and required installation space for the radiation emitter and receiver, which are preferably structured as SMD (surface mounted device) components, is reduced, so the housing of the sensor device can be structured to be generally shallower.
According to a further embodiment of the invention, a spacer is provided, extending between the circuit board and the wall and thus defining distances from the radiation emitter and receiver to the respective radiation guide elements.
As mentioned above, it is also an object of the present invention to provide a method of producing a sensor device that can be carried out inexpensively and by simple manufacturing technology.
To achieve this object, a method for producing a sensor device to be attached to a side of a light-transmissive pane of a motor vehicle by a transparent coupling medium, the sensor device having at least one radiation guide element which conducts radiation between a radiation emitter and/or a radiation receiver in a housing and an opposite side of a light-transmissive pane, involves: forming together as one piece of resinous plastic the at least one radiation guide element with a wall of the housing bordering the radiation guide element by an, at least, two-stage injection molding operation. In this regard, either the radiation guide element is molded of a transparent plastic material in a first stage, and then in a second stage a non-transparent plastic material is injected onto and about it to form the wall, or in a first stage the wall is molded of the non-transparent plastic material, forming at least one opening, and in a second stage the radiation guide element is molded onto an edge of the wall defining the opening.
A particular advantage of the method of this invention is that a carrier module of a plurality of radiation guide elements and non-transparent blocking elements surrounding them in an airtight manner can be easily produced, and this carrier module can be attached as a cover in a form-fitting and/or non-positive manner to a pot-shaped part to form a housing. Because the radiation guide elements are connected as one piece with the non-transparent blocking element, the number of components can be reduced. The carrier module thus formed creates a flat surface, so that a transparent coupling medium arranged between the carrier module and the pane may be arranged in a uniformly distributed manner. Because the radiation guide elements are held in openings of the blocking element by being integrally molded or sheath-injected therewith, an intimate and secure connection is created. The carrier module produced in this way has dimensional stability and permits a compact design of the sensor device.